1. Field of the Invention
The present invention relates to a data reproduction apparatus for an optical disc system.
2. Description of the Related Art
FIG. 1 is a block diagram showing a data reproduction apparatus for a conventional optical disc system. In the FIG. 1 apparatus, a radio frequency (RF) signal read from an optical disc is input to an analog-to-digital converter (ADC) 11 and a binarization circuit 14. The binarization circuit 14 binarizes the RF signal and outputs the binarization signal to a phase locked loop (PLL) 15. The PLL 15 receives the binarization signal and generates a clock signal PLCK synchronized with the RF signal. The clock signal PLCK is supplied to the ADC 11, a waveform equalizer 12 and a Viterbi decoder 13. The ADC 11 converts the input analog RF signal into a digital RF signal and outputs the digital RF signal to the waveform equalizer 12. The waveform equalizer 12 receives the digital RF signal and waveform-equalizes the received digital RF signal into a form which is appropriate for the Viterbi decoder 13. The Viterbi decoder 13 receives the waveform equalized signal to then be Viterbi decoded and outputs the result as a reproduction signal (VITO). The Viterbi decoding can restore the damaged signal when the RF signal is damaged due to noise interference in a channel, such as that which is widely used in a hard disc drive (HDD).
However, if in the input RF signal in the conventional data reproduction apparatus is asymmetrical, the Viterbi decoder does not restore the RF signal, thereby degenerating the quality of the reproduced data.